Looks like they were in Bureau Co, IL, in 1940 census...
Robert L Hancock, 37, born KY
wife Lillian, 35, born IL
son William, 8, born IL
daughter Roberta, 7, born IL
son Jerry, 4, born IL
son Donald, 10 months, born IL
Record a little confusing as it shows Robert's residence in 1935 was Raywick, KY, but Lillian and William show as Princeton, Bureau Co, IL.
Here is death record of Robert Hancock, Jr.https://familysearch.org/pal:/MM9.1.1/NQ4D-7NG
Death record for son John Hancock:https://familysearch.org/pal:/MM9.1.1/NQPW-2FM